[MlMt] Rule Condition to Limit to a Source Mailbox

[Gary Hull]

I don't like to have mails lurking around in the archives and the like 
without being marked as Seen, even if "Seem" means that I decided not to 
look at them. When I look in my Unread folder under Mailboxes, there are 
two cases that I'd like to automate with a rule to mark them as seen:

1. Stuff that I've glanced at for a fraction of a second and then 
clicked the Archive button. The time viewed is not sufficient to mark 
them as Seen

2. Junk mail marked as junk by one of the mail providers I use, but 
which SpamSieve hasn't marked as junk.

I can easily recognize these two types of mail when I look in the Unread 
mailbox: Archived mail begins with "Archive - " in the Source Mailbox 
column, and junk mail begins with "Spam - " in the Source Mailbox 
column. I can't figure out how to filter by source mailbox in the Rules 
Conditions dialog for the Unread mailbox. How to do this?